1. Field of the Invention
The present invention relates to a defect inspection apparatus, a defect inspection method, and a semiconductor device manufacturing method.
2. Related Background Art
As a method for inspecting the result of a circuit pattern formed on a semiconductor wafer, there is used a method of using a Scanning Electron Microscope (SEM), scanning the top of the wafer with an electron beam, using an SEM image of the circuit pattern obtained by detecting resultant secondary electrons, reflected electrons and back scattering electrons (hereafter referred to as “secondary electrons and the like”), comparing, for example, SEM images of adjacent circuit patterns with each other, calculating a difference between them, and thereby detecting a defect. (For example, Application of μloop™ Method to Killer Defect Detection and In-line Monitoring for FEOL Process of 90 nm—node Logic Device, Akihiro Shimada, Yasuo Matsumiya, Atsuo Fushida, Atsuo Shimizu, Fujitsu Limited, Akiruno Technology Center (hereafter referred to as “non-patent document 1”) and In-line Inspection Resistance Mapping Using Quantitative Measurement of Voltage Contrast in SEM images, Miyako Matsui, Yoshihiro Anan, Takayuki Odaka, Hiroshi Nagaishi, and Koichi Sakurai, Central Research Laboratory, Hitachi Ltd., Renesas Technology Corp. (Proc. Of SPIE Vol. 6922, 692218, 2008) (hereafter referred to as “non-patent document 2”.))
According to the methods-disclosed in non-patent document 1 and non-patent document 2, pattern defects (open circuits and short circuits) and particles existing in the circuit pattern on the wafer surface are detected as shape contrast or material contrast, and electric defects (open circuits and short circuits) existing on the wafer surface or in an underlying layer are detected as potential contrast of the circuit pattern on the wafer surface.
However, inspection using an electron beam has a problem that inspection time is long, and a higher speed is demanded strongly. On the other hand, inspection using an electron beam has an advantage that inspection can be conducted with high resolution as compared with optical inspection. Improvement of the detection sensitivity of minute defects making the most of this advantage is demanded.
For making the inspection faster, it is necessary to acquire a SEM image without decreasing the signal quantity from a defect by conducting scanning fast with a beam of a large current. On the other hand, for detecting a minute defect, it is necessary to improve the resolution by using a small current to reduce blurring caused by the space charge effect and narrowing down the beam spot size.
In this way, inspection speed increase and resolution improvement are in the relation of trade-off in the conventional inspection technique of SEM scheme. It is difficult to simultaneously achieve both objects contradicting each other because of a physical limit.
In order to solve the above-described problem, there is proposed a method for reducing the number of times of beam scanning and the number of times of stage movement and making the inspection fast by using a rectangular beam which is larger in cross-sectional area than the SEM beam as the electron beam for scanning the wafer and moving a stage in the major axis direction with a pitch coinciding with the length of the major axis length while scanning in the minor axis direction of the rectangular beam by using a deflection system (for example, Japanese Patent Laid-Open Pub. No. 07-249393 (1995)). According to the method disclosed in Japanese Patent Laid-Open Pub. No. 07-249393 (1995), the number of times of beam scanning and the number of times of turn-back are reduced to 1/N because the beam shape is N times long (the area increases) in the major axis direction.
However, the method disclosed in Japanese Patent Laid-Open Pub. No. 07-249393 (1995) is a method which produces the effect when an inspection apparatus of map projection scheme is used and a two-dimensional image can be acquired in the lump without scanning with a beam. If it is attempted to apply the method to an apparatus of SEM scheme simply, the resolution is degraded remarkably, resulting in a problem of poor practicality.
More specifically, according to the method disclosed in Japanese Patent Laid-Open Pub. No. 07-249393 (1995), the resolution in the stage movement direction (Y direction) is remarkably deteriorated due to the magnitude of the size of the electron beam in the stage movement direction as length ΔY in the longitudinal direction. For a high-speed inspection, a wide deflection and a high speed scanning are necessary for an inspection apparatus using an electron beam. However, when it is attempted to perform a wide deflection and a high speed scanning by use of a SEM system apparatus through the method disclosed in Japanese Patent Laid-Open Pub. No. 07-249393 (1995), a blur in the beam scanning direction (X direction) would generate due to deflection aberration and distortion in the beam scanning direction (X direction) would generate from problems of scanning power supply and electrostatic charge due to a high speed scanning.